ADRB1 and familial dilated cardiomyopathy: In addition, studies on β1-adrenergic receptor (β1-AR) autoantibodies (β1-AAbs) have indicated that active immunization with synthetic peptides corresponding to the second extracellular loop of the β1-AR induces a marked production of β1-AAbs, which have similar biological and immunological properties as in the plasma of DCM (dilated cardiomyopathy) patients21.